Transformer for electric discharge lamps



Nov. 15, 1960 c. E. STRECKER 2,960,624 TRANSFORMER FOR ELECTRIC DISCHARGE LAMPS Filed May 27, 1959 (flaw/as 5 Strec/fez:

provision of a high initial starting voltage.

ance.

the operation of the lamps.

United States Patent TRANSFORMERFOR ELECTRIC DISCHARGE LAMPS Qharies E. Strccher, deceased, late of Danville, 111., by Jeanne 1E. fitrecirer, executrix,'Danville, 113., assignor to General Electric Company, a corporation of New York Filed May 27, 1959, SeraNo. 816,342

11 Claims. (Cl. 31597) This invention relates to electric discharge lamps, and more particularly to ballast transformer apparatus for starting and operating such lamps.

It is a characteristic of electric discharge lamps, such as fluorescent lamps, that their internal resistance do creases as the current flow therethrough increases. It is, therefore, necessary in the installation of such lamps to provide means which will limit the currentflow through the lamp to a safe value. "In addition, it mayalso be desirable to'provide a'higher voltage-forinitially starting or causing a discharge in the lampth-an'is conveniently available. When electric discharge devices are operated on alternating current, it is conventionalpractice to provide a single high 'reactance ballasttransformer toprovide these two functions, i.e., current limiting and the Such a transformer provides-an open circuit voltage for starting and also, by virtueof its "high reactance, provides in.- pedance during normal operation to limit the current flow.

A high 'reactance transformer is one in which the primary and secondary windings areloosely coupledso that when the transformer is carrying load, there is a substantial amount of leakage flux and the voltages in duced in the windings by this leakage flux cause the transformer to have a relativelyhigh effective series reactance, or what is commonly'known'as leakage reactwindings on a diiferent'part of the -magneticcore and to provide a magnetic shunt-between thewindirrgs thereby providing a path for the leakage'fiux. Thisshunt is usually provided with an air'gap so calibrated -thatthe operating current of the secondary core of the transformer will be limited to the desired value. The high starting'voltage can be achieved by'using'a'transformer with the winding connected as an autotransformer, i.e., the primary and secondary are connected in series across at least one of the lamps so that'their voltages are additive.

It will be seen that, since the output Voltage may be reduced after the device has started/the autotransformer connection may become unnecessary and, in fact, un-

desirable. While autotransformer connections will greatly aid in the starting of the discharge devices, such connections 'resultin relatively'highvoltages which are not desired for lamp operation. It will also be seen that it is advantageous to 'have the primary and secondary of the transformer connected as an autotransformer across at least one of the lampsfor'thestarting operation and "as substantially isolated transformer connections for Foroptimum efficiency, this change should be automatic and not require additional switches and the'like.

It is, therefore, an object'of this invention to provide an improved *ballast transformer apparatus for starting and operating electric discharge lamps which will incorporate the desirable :features set:forth above.

The conventional way of constructing such a transformer is to arrange the primary and secondary electrodes of one of the lamps during starting.

as great.

Patented Nov. 31. 5, 3930 ice A more specific object of this invention is to provide an improved ballast transformer apparatus for starting and operating a pair of discharge lamps which will place the combined voltage of the primary and secondary windings across at least one of the lamps during starting thereof, and which will thereafter function as a substantial isolated secondary across the lamps.

Further objects and advantages of this invention will become apparent and the invention will be better understod by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this Specification.

This invention, in one embodiment thereof, includes a transformer haivn the secondary connected across a pair of serially connected discharge lamps. The primary and the secondary of the transformer are connected in series and in autotransformer relation, so that their open circuit voltages during starting are additive, by means of a line containing a fairly high impedance such as a starting impedance or capacitor. The additive voltages of the primaryand thesecondary will be applied across the The lamps maybe in capacitive relation to a conducting part or fixture grounded to the low potential side of the line as a starting aid. The starting capacitor also functions to place the-combined voltages of the. primary and the secondary across the capacitive coupling between one lamp electrode and the conducting fixture. As is wellhnown, a fairly small current will then flow through the electrode of the first lamp to the fixture, and this small current will bring about increased ionization in the area about the electrode. The increased ionization, which may be in cooperation with the heating of the electrodes,

will cause a breakdown of the gas contained within the device. After the first lamp starts, the second of the series connected lamps will start from the combined voltage ofthe secondary winding and the first lamp voltage, which is equal to the voltage across the high impedance plus the voltage across the primary winding.

Consequently, "both lamps -make use of the primary winding voltage during starting. Once the lamps start,

"the only way for a circuit to be completed between the primary and'the secondary of the transformer is through the high impedance and, since the impedance will not carry any appreciable load current, instead of an autotransformer the connections will 'be substantially those of an ordinary isolated transformer. The main part of the current will pass through the device and the secondary in closed circuit; the current through the lamp tothe fixture and the current passed through the lamps from the primary through the-starting capacitor will be minor with lamps to start the lamps, the secondary may be made smaller since the output voltage therefrom need not be Also, the autotransformer connection, which becomes undesirable once the lamps have started andare operating, is not effective after starting to make the primary and secondary voltages additive across the lamps.

In the drawing, Fig. l is a schematic diagram of an improved ballast transformer and circuit for a .pair of serially connected discharge lamps incorporating the features of the present invention;

Fig. 2 is a plan view of a ballast transformer apparatus according to the instant invention;

Fig. 3 is a simplified schematic diagram of the circuit of Fig. l, omitting the cathode heating winding for clarity; and,

Fig. 4 is a simiplified schematic diagram illustrating an equivalent grounding connection between the low potential side of the input line and the lamp fixture.

Referring now to Figs. 1, 2 and 3, a ballast transformer apparatus according to the instant invention is shown connected to a pair of serially connected rapid-start lamps. The transformer apparatus consists of an iron core 1 comprising a central winding leg 2 and an enclosing yoke 3 within a case or housing 4. On the central Winding leg is a primary winding P, a secondary winding S and cathode heating windings H H H As shown, the cathode heating winding H is an extension winding of the primary P. The primary winding P, the secondary winding S and heating windings H H and H are all on the common magnetic core 1 and are, therefore, in inductive relation with each other. The primary winding P has a pair of leads 5, 6 for connection to an alternating current voltage supply source 7, 8. As hereinafter explained, such a supply source as used for residential and commercial distribution in this country, normally, although not necessarily, has the low potential side 7 thereof grounded, for example, through ground 9. An electrically equivalent circuit where the low potential side of the supply source is not grounded is illustrated in Fig. 4 and will be hereinafter discussed. Referring again to Figs. 1 and 2, the secondary winding S has leads 10, 11 for connection across a pair of serially connected lamps L L The lamps, as normally installed, are in close proximity to a grounded conductive part or fixture 12 grounded through ground 13 and therefore in electrical circuit with the low potential side 7 of the supply source 7, 8. In one lead 11 of the secondary S is a capacitive reactor 14 of large capacitance, which may be sufficient, if desired, to draw leading current through the transformer during operation of the lamps. The capacitive reactor 14 is therefore serially connected with the secondary S.

Each heating winding has a pair of leads for connection to one or more of the electrodes of the discharge lamps. Heating winding H has leads 15, 16 for connection to electrode 17 of lamp L and electrode 18 of lamp L Heating winding H has a pair of leads 1,'20 for connection to electrode 21 of lamp L Heating winding H has a pair of leads 22, 23 for connection across electrode 24 of lamp L As is well-known in a'rapid-start type fluorescent lamp, the electrodes 17, 18, 21 and 24 are continuously supplied with heating current by the heating windings H1, H and H The high potential side 6 of the primary winding P is connected in circuit relationship with the low potential side of secondary S so as to connect the primary winding P and the secondary winding S in autotransformer relationship with their open circuit voltages in adding relation. The circuit means connecting the high potential side of the primary winding P and the low potential side of the secondary winding S includes line 25 having therein a starting capacitor 26. The circuit means connecting the primary winding and the secondary winding, as shown, connects the secondary lead 11 on the side remote from the capacitive reactor 14 in a first starting loop as explained below.

It may be desirable, but not necessary, to connect the low potential lead of the primary P to the transformer case 4 through a high resistance 27, which may be in the order of one megohm. Since the transformer case 4 is characteristically secured to the lamp fixture12, this connection insures the lamp fixture 12 being 'at the same potential as the low potential lead 5. As hereinafter'explained, in a normally grounded system, this resistor performs no electrical function and acts merely to safeguard against an improperly grounded system. It does, however, permit operation of an ungrounded system.

The primary P and secondary winding S may be placed side by side on the central winding leg 2 of the magnetic core 1, thereby resulting in leakage reactance in the magnetic circuit. Where it is desired to increase the magnetic leakage and therefore the leakage reactance of the transformer, this may readily be accomplished by the inclusion of high reluctance flux leakage paths or shunts in the core 1 between the primary winding P and the secondary Winding S. It will be understood that, depending upon the design of the transformer, the flux leakage paths may be formed either through nonmagnetic material such as air, or through magnetic material as by the provision of the projecting shunt legs 28 formed on the core. It will be noted that there are gaps between the ends of the shunt legs 28 and the center leg 2 to provide high reluctance in the leakage paths of the illustrated transformer. This shunt construction results in what is known as a high reactance transformer and the transformer acts to limit the current flow in the circuit including the secondary winding and the discharge lamps. As heretofore explained, this is necessary due to the negative resistance characteristic of the lamps.

Referring now to the simplified circuit of Fig. 3 Wherein the heating windings H H and H have been omitted, the operation of the instant transformer will now be explained. With the primary P connected to a source of grounded alternating current voltage, the conductive fixture 12 is connected through its ground 13 to the low potential side of the supply voltage 7. The lamps L L in close proximity to the grounded conductive fixture 12 are in capacitive relation therewith. With neither lamp burning, a first starting loop including lamp L includes the primary P, line 25, starting capacitor 26, capacitive reactor 14, the secondary S, line 10, line 22, lamp L and line 16, thereby placing the total additive voltages of the primary P and the secondary S across lamp L A starting aid potential circuit also uses the combined voltages of the primary and secondary windings. Such a starting aid loop includes the conductive fixture 12, through ground to the low potential lead 5 of primary P, primary P, through starting capacitor 26, secondary S, through electrode 24 of lamp L A fairly small current will flow from the electrode 24 of lamp L which is at the highest potential with respect to the grounded fixture, and this small current will bring about an increased ionization in the area around the electrode. The increased ionization, in cooperation with the heating of the electrodes, will cause a breakdown of the gas contained within the device. The added voltage of the primary P and the secondary S across the lamp L is then sufiicient to start lamp L Once the lamp starts, however, the only way for a circuit to be completed between the primary P and the secondary S is through the starting capacitor 26. Since the capacitor 26 is of relatively low capacitance, no substantial operating current can flow through this connection.

After lamp L has started, lamp L will then start from the voltage of the secondary winding S and the voltage of lamp L The voltage of lamp L is equal to the voltage across the starting capacitor 26 plus the primary voltage P. Consequently, lamps L and L make use of the voltage in the primary winding P in getting started.

With both lampsL and L started, the operating loop includes the secondary winding S, lamps L and L and the capacitive reactor 14 in substantially isolated series circuit. The high impedance of the starting capacitor 26 makes the starting circuit virtually ineffective once both lamps have started, because relatively small current only can flow through the starting capacitor. Thus, the lamps L and L are operated from essentially an isolated secondary type transformer. i i

Fig. 4 is a simplified schematic diagram of an apparatus aae esa according to the instant invention where neither of the supply lines '7, 8 are grounded. The transformer circuit is substantially the same as that described above except for the starting aid connected to the conductive fixture.

As is well-known, in this country it is customary for most residential and commercial electrical distribution systems to have the low potential side of the distribution line grounded. It is also customary for the fixture in which the lamps are mounted to be grounded. In particular, the fixture is normally an elongated grounded conducting part. The effect of the grounding of one side of the lines and the fixture in which the lamp is mounted is to place the lamp fixture in electrical connection with the low potential end of the primary winding so that the lamp and fixture are in capacitive relation, thereby facilitating starting of the lamp as explained above. However, in the event that one side of the distribution system is not grounded or in the event that the lamp fixture is not grounded the low potential side of the distribution system or supply source may be electrically connected to the conducting fixture. In such a case, a high resistance may, if desired, be provided between the low potential side of the supply line and the fixture. Such a high resistance may be preferably on the order of at least one megohm. Such a resistor is normally connected between the low potential side of the input line and the ballast transformer case. Since the ballast transformer is normally mounted on the conductive fixture and in electrical circuit therewith, this supplies theaforesaid grounded connection. It is to be understood, however, that if the fixture is grounded and the low potential side of the input line is also grounded, this resistance provides no starting or operating function. In the event of a normally ungrounded line, an electrical connection is normally made from the low potential side of the line to the fixture in order to function as the aforesaid starting aid. The aforesaid resistance provides the further function of preventing a lethal flow of current from the device to the ground in the event that the low potential-side of the input line is not grounded; and it will prevent firing of the lamp through ground in the event that the grounded side of the lamp is opened.

As described above, the fixture 12 is normally grounded, and the low potential side of the line (7, Fig. 3) is normally grounded. However, if it is desired to apply the instant invention to a rapid-start series circuit wherein either the source of supply voltage or the fixture is ungrounded, it is merely necessary to electrically connect the conductive fixture 12 in circuit relation with the low potential side 7 of the supply source as illustrated by line 29. If desired, line 2% may include a high resistance 27 as hereinbefore explained. As normally connected, the low potential side 7 of the supply source would be connected to the transformer case through resistance 27, and the transformer case would be electrically connected to the conductive fixture 12 as indicated schematically by line 29. The lamps L L are then in capacitive relation with the fixture 12 and the circuit operates substantially as described above.

It is also to be understood that the instant invention may be applied equally to a lag circuit as well as to a lead circuit. For this reason, the modification of Fig. 4- is shown without a capacitive reactance serially con nected to the secondary, as was illustrated in the modification of Figs. 1 and 3.

It will further be understood that while the circuits herein illustrated utilize a ballast transformer having a high reactance, the invention may be used advantageously where a low reactance transformer is used with other ballasting means being provided. Also, while a rapidstart lamp circuit has been shown, that is, electrodes are continuously heated before and after starting, the invention may be advantageously applied to other types of lamp circuits, for example, to an instant start lamp circuit. Therefore, while this invention has been explained :6 by describing particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as described in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. Ballast transformer apparatus for starting and operating at least one fluorescent lamp having two spaced electrodes at the respective ends of the lamp and comprising a magnetic core having a primary winding and a secondary winding thereon, a pair of input lines on said primary winding for connection to a source of alternating current, output lines on said secondary winding for respective connection to the electrodes of said lamp, a starting impedance connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being connected by said impedance in voltage adding relation, and means for connecting the low potential end of said primary winding in circuit with said lamp whereby said transformer apparatus provides autotransformer type high voltage across the lamp for starting and isolated transformer type running voltage across said lamp after starting.

2. Ballast transformer apparatus for starting and operating at least one fluorescent lamp mounted near a conductive part and having two spaced electrodes at the respective ends of the lamp comprising, a magnetic core having a primary winding and a secondary winding thereon, a pair of input lines on said primary winding for connection to a source of alternating current, a pair of output lines on said secondary winding for respective connection to the electrodes of said lamp, a starting impedance connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, means including said impedance for connecting the low potential end of said primary winding in circuit With said lamp whereby saidtransformer apparatus provides autotransformer type starting voltage across said lamp and isolated transformer type voltage across said lamp after starting, and means for connecting the low potential end of said primary winding in circuit with said conductive part whereby to place said lamp in capacitive relation with said fixture to provide starting aid potential to said lamp for starting thereof.

'3. A ballast transformer apparatus according to claim 2 above wherein said means for connecting the low potential end of said primary winding in circuit with said conductive part includes grounding means.

4. Ballast transformer apparatus for starting and op erating a pair of serially connected fluorescent lamps, comprising a magnetic core having a primary winding and a secondary winding thereon, a pair of input lines on said primary winding for connection to a source of alternating current, a pair of output lines on said secondary Winding for connecting the secondary winding serially across the pair of serially connected lamps, a starting capacitor connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, and means for connecting the low potential end of said primary winding in circuit with each of said lamps whereby said transformer apparatus provides autotransformer type starting voltage across one of said lamps during starting thereof and i olated transformer type running voltage across said lamps after starting thereof.

5. Ballast transformer apparatus according to claim 4 above and including a capacitive reactor serially connected with said secondary winding to provide leading current in said transformer.

6. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conductive fixture and having two spaced electrodes at the respective ends of each of said lamps comprising, a magnetic core having a primary winding and a secondary winding thereon, a pair of input lines on said primary winding for connection to a source of alternating current, a pair of output lines on said secondary Winding for respective connection to the electrodes of said lamps for connecting said pair of serially connected lamps serially in circuit with said secondary winding, a starting capacitor connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, means for connecting the low potential end of said primary winding in circuit with each of said lamps whereby said transformer apparatus provides autotransformer type starting voltage across one of said lamps for starting said lamps and isolated transformer type running voltage across said lamps after starting said lamps, and circuit means for connecting the low potential end of said primary winding in circuit with said conductive fixture whereby said lamps are in capacitive relation with said fixture to provide starting aid potential to said lamps during starting thereof.

7. Ballast transformer apparatus according to claim 6 wherein said means for connecting the low potential end of said primary winding in circuit with said conductive fixture includes grounding means.

8. Ballast transformer apparatus for starting and operating a pair of serially connected fluorescent lamps mounted in a conductive fixture and having spaced electrodes at the respective ends of said lamps comprising, a magnetic core having a primary winding and a secondary winding thereon, means providing leakage reactance between said windings, a pair of input lines on said primary winding for connection to a source of alternating current, a pair of output lines on said secondary winding for connecting said secondary winding in a series operating circuit with said serially connected lamps, a starting capacitor connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, means for connecting the low potential end of said primary winding in circuit with each of said lamps whereby said transformer apparatus provides autotransformer type starting voltage across one of said serially connected lamps during starting thereof and thereafter provides isolated transformer type running voltage for said lamps after starting thereof, and means including a high ohmage resistor for connecting the low potential end of said primary winding in circuit with said conductive fixture whereby said lamps are placed in capacitive relation with said fixture thereby to provide starting aid potential to said lamps during starting thereof.

9. Ballast transformer apparatus for starting and operating a pair of serially connected hot cathode type fluorescent lamps mounted in a conductive fixture and having spaced electrodes at their respective ends comprising, a magnetic core having a primary winding and a high voltage secondary winding thereon, means for providing leakage reactance between said primary and said secondary windings, a pair of input lines on said primary winding for connection to a source of alternating current, a pair of output lines on said secondary winding for serially connecting said secondary winding in a series circuit with said pair of serially connected lamps, a first cathode heating winding on said core, a second cathode heating winding on said core, a third cathode heating winding on said core, a pair of output lines connected to the first cathode heating winding for connecting the winding across one of the cathodes of each lamp, a pair of output lines connected to the second cathode heating winding for connection across the second electrode of one of said lamps, a pair of output lines connected to the third cathode heating winding for connection to the second electrode of said second lamp, a high capacitive starting capacitor connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, means for connecting the low potential end of said primary winding in circuit with each of said lamps whereby said transformer apparatus provides autotransformer type starting voltage across one of said lamps during starting thereof and isolated type transformer running voltage across the lamps after starting thereof, and means for connecting the low potential end of said primary winding in circuit with said conductive fixture thereby to complete an electrical path across said primary and said secondary windings through said lamp and fixture during starting thereof to provide starting aid potential therefor, the current through said starting aid potential circuit being minor with reference to the current through said lamp from said secondary winding after starting thereof.

10. An electric lighting system comprising a conductive part, a pair of serially connected fluorescent lamps mounted alongside said part, a high reactance ballast transformer comprising a magnetic core having a primary winding and a secondary winding thereon, said secondary winding being serially connected in a series circuit with said serially connected lamps, a starting capacitor connected between the high potential end of said primary winding and the low potential end of said secondary winding, said windings being wound and connected in voltage adding relation, circuit means connecting the low potential end of said primary winding with said lamps whereby said transformer apparatus provides autotransformer type starting voltage across one of said lamps during starting thereof and isolated transformer type running voltage across said lamps after starting thereof, and circuit means connecting the low potential end of said primary with said conductive fixture to provide starting aid potential to said lamps during starting thereof.

11. An electric lighting system according to claim 10 wherein said circuit means connecting the low potential end of said primary winding to said conductive fixture includes grounding means.

References Cited in the file of this patent 'UNlTED STATES PATENTS 2,824,263 Strecker et al. Feb. 18, 1959 2,869,037 Brooks et al. Ian. 13, 1959 FOREIGN PATENTS 705,081 Great Britain Mar. 10, 1954 

